1. Field of the Invention
The present invention relates generally to lifting devices, and more particularly, to a wheelchair lift device to provide access to stages, platforms, risers and other elevated structures for individuals with disabilities.
2. Description of the Background Art
Under the Americans With Disabilities Act of 1990 (the “ADA”), the U.S. government required that public buildings be accessible to the disabled. For persons requiring a wheelchair for mobility, abrupt changes in floor elevation have to be modified to enable access by wheelchair. The ADA permits vertical lifting devices to be used instead of a ramp.
Lifting devices for the disabled are known in the prior art. For example, U.S. Pat. No. 5,105,915 (Gary) describes a lifting device having a car including fixed sides and short, one-piece ramps at each end. The car is raised and lowered by a pantograph jack including a hydraulic pump driven by an electric motor controlled by switches. The patent also describes several lifting devices of the prior art. Another wheelchair lifting device is disclosed in U.S. Pat. No. 6,182,798 to Brady, et al., and assigned to AGM Container Controls, Inc., the assignee of the present invention. The '798 patent discloses a lift device with gates at both ends of the lift car, transparent walls, a loading ramp, a dock plate, a stage height sensor, and numerous safety features. In addition, U.S. Pat. No. 7,926,618, also assigned to the assignee of the present invention, discloses a lift device suitable for elevating wheel chair-bound individuals to stages or platforms.
In many cases, wheel chair lifting devices can obstruct the view of persons in an audience at an event, particularly when the lift device is in its fully-elevated position. While it is important for those who are disabled to be able to have full access to stages and platforms within auditoriums, the lifting devices used to serve those who are handicapped should not become a viewing obstacle to others in attendance. Some lift devices employ relatively high towers, often in conjunction with idler gears and drive chains, to elevate a wheel chair lift car, and such towers tend to obstruct the surrounding view even when the lift car is fully lowered. Other lift devices are known which avoid the need for towers, but the lifting mechanism includes moving parts that need to be shielded to avoid injury to persons nearby, and to avoid interference with foreign objects that might find their way below the lift car. As an example, in assignee's U.S. Pat. No. 7,926,618, no towers are required, but pivoting hydraulic cylinders positioned on opposing sides of the lift car, and the hydraulic hoses attached thereto, must all be shielded from body parts and/or foreign objects, as by a pleated “skirt”, which extends upwardly from the floor to the base of the lift car as the lift is elevated. Within U.S. Patent Application Publication No. 2008/0308358, also assigned to assignee, such a protective skirt is disclosed, along with sensors for detecting that a person, or object, has fallen against such protective skirt.
Moreover, while the lift device disclosed in assignee's U.S. Pat. No. 7,926,618 maintains a relatively low profile, elevation of the lift car requires movable intermediate members that are slidingly engaged with a lower fixed vertical track; the lift car is, in turn, slidingly engaged with such intermediate members. It would be preferred to avoid the need for such intermediate members to minimize expense and parts counts, while allowing the lift platform to be directly raised from a base. In addition, past efforts to provide a lift device having a low profile have included orientation of the hydraulic cylinders at an angle to the vertical; however, when lifting cylinders are oriented at an angle to the vertical, the force vector exerted in the upward direction is reduced, thereby requiring heavier, more-costly hydraulic cylinders, pumps, and motors, to provide the necessary lifting force. No matter what lifting system is utilized, it is obviously important to keep the lift car stable at all times, particularly when the lift car is elevated, to avoid injury to occupants.
Lift devices are known wherein the lifting forces are applied directly below the platform of the lift car that supports the occupant of the wheel chair. One advantage of lift devices is that the load borne by the platform of the lift car is directly supported by the lift mechanism. On the other hand, locating the lift mechanism directly below the lift platform presents a disadvantage. The lift mechanism always presents some thickness or depth, even when the lift is lowered, and by locating the lift mechanism directly below the lift platform, it is then virtually impossible to fully-lower the floor of the lift car flush with the floor. Accordingly, a loading ramp must then be provided to raise the wheel chair occupant from the ground up a few inches to the lift car floor when boarding the lift device. The loading ramp adds weight, cost, and complexity to the lift device.
One alternate technique which has been used in the past to avoid the need for a loading ramp is to house the lifting mechanism on the sides of the lift platform, rather than below the lift platform itself. However, applicant has discovered that, in certain circumstances, this alternate technique presents its own set of problems. When the lifting forces needed to elevate the lift car are applied to the sides of the lift car, the load borne by the floor of the lift car is transferred to the sides of the lift car. Under sufficient load, the floor of the lift car tends to bow downwardly. This bowing of the lift car floor exerts a torque upon the attached side walls of the lift car. As a result, the upper portions of the side walls of the lift car, which originally extended essentially vertically above the lower portions thereof when the lift car was lowered to the ground, now tilt inwardly toward each other. Angular deformation of the side walls of the lift car is problematic; for example, inward pressure exerted by the side walls upon the front entry gate (used when the lift is lowered) and the rear exit gate (used to exit the lift when raised to stage height) can “pinch” those gates, making them more difficult to open.
Wheel chair lift devices are often used repeatedly in conjunction with the same stage or platform, whereby the lift car is elevated numerous times to the very same height. It is therefore desirable to provide a control mechanism by which the maximum elevational height of the lift can be set in advance, or programmed, thereby automatically stopping the lift at the stage height repeatedly and consistently. The wheel chair lift device disclosed in assignee's prior U.S. Pat. No. 7,926,618 discloses a height adjustment mechanism accessible through a panel of the lift car for varying the elevational height of the lift. A rotatable arm is used to set the elevational height, and a knob secured to the end of such rotatable arm slides within a circular slot. The knob can be loosened to move the knob within the circular slot, thereby repositioning the rotatable arm. Once the knob is set to the desired elevational height, the knob is re-tightened, and the access panel is closed.
An alternate height adjustment mechanism is disclosed in assignee's U.S. Pat. No. 7,721,850 for use with a fixed-installation lift, wherein a cable attached to an actuator moves the actuator as the lift car moves, the actuator eventually engaging a microswitch when the lift reaches the desired maximum height. Adjustment of the maximum desired height requires an installer to adjust the relative position of the microswitch along a rail traversed by the actuator.
Portable wheelchair lifting devices generally require that the height to which the lift car is elevated be readily adjustable. Such lift devices are frequently moved from one stage or platform to another, and the elevations of two or more stages or platforms often differ from one another. On the other hand, once a portable lift is transported to a particular location, and the maximum height has been re-adjusted to suit the particular platform or stage at the new location, further height adjustments are neither required nor recommended.
Therefore, it is important to be able to quickly and easily adjust the maximum height to which the lift is elevated each time the lift is moved to a different platform or stage. Once the maximum height is set for the new stage or platform, it is also important that the lift should be able to raise the platform of the lift device repeatedly, and reliably, to the pre-set maximum height. Clearly, it would be advantageous to be able to verify that the mechanism used to signal that the maximum height has been reached is, in fact, operational before permitting the lift car to elevate; if the maximum height detection system is not working properly, and the lift is permitted to be elevated, the lift will not automatically stop when it reaches the desired maximum height.
In view of the foregoing, it is an object of the present invention to provide a wheel chair lift device suitable for lifting wheelchair-bound users up to the height of stages, platforms, risers and the like in a safe and reliable manner, and comporting with all applicable ADA requirements.
Another object of the present invention is to provide such a lift device which has a relatively low profile to avoid interference with viewing by an audience and/or spectators in an auditorium or other facility where events are held.
Still another object of the present invention is to provide such a wheel chair lift device which makes efficient use of forces applied by hydraulic cylinders to minimize the size, weight and cost of such hydraulic cylinders, and the pump and motor used to power them, while still supporting the lift car in a stable manner.
Yet another object of the present invention is to provide such a wheel chair lift device which minimizes the number of exposed moving components around and below the lift device.
A further object of the present invention is to provide such a lift device which does not require a protective skirt to protect persons nearby from injury and/or to shield foreign objects that would otherwise become caught within the lifting mechanism.
A still further object of the present invention is to provide such a lift device which avoids the need for chains or gears in order to raise or lower the lift car.
Another object of the present invention is to provide such a lift device that is relatively inexpensive, easy to construct and use, and simple to maintain.
Still another object of the present invention is to provide such a lift device that is provided in a form that is easy to transport, and which can be collapsed to pass through narrow openings.
Yet another object of the present invention is to provide such a lift device wherein the lift car floor can be sufficiently lowered to the ground to avoid the need for an entry ramp, while avoiding deformation of the lift car side walls away from their usual vertical orientation.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.